Voice current repeater circuits



Aug. 29, 1933. l E. K. SANPEMAN ET AL 1,924,131

VOICE CURRENT REPEATER CIRCUITS Filed 001'.. 3, 1950 3 Sheets-Sheet 1 FlG.

@hid wils INVENTOR Aug 29, 1933- E. K. sANDl-:MAN ET AL 1,924,131

VOICE CURRENT REPEATER CIRCUITS Filed OCI'.. 3, 1930 3 Sheets-Sheet 2 FIG. 3

PHILIP R. THOMAS- CARLTON R. DUNHAM ATTORNEY Aug 29, 1933 E. K. SANDEMAN Er AL '1,924,131

VOICE CURRENT REPEATER CIRCUITS may 56' lNvENToR EDWARD K.SANDEMAN PHluP R .THOMAS CARLTONRDUNHA BWQ i A TORNEY Patented Aug. 29, 1933 STATES "11,924,131 VoroE CURRENT yitEPEA'iER CIRCUITS nawam Kenneth sanaemam Philip 'Robert Thomas, vand Carlton Rosslyn Dunham, London, England, `assignors to International `Standard Electric Corporation, N. Y.,'a Corporation of Delaware.

New York,

. Application October 3, 1930, Serial No. 486,130,

, andin Great Britain Octoberl), 1929 s claims. (ci. 17e- 170) so'that transmission may take place in the other direction with the desiredainpliiication.

According to one feature of the invention, the telephone signals are repeated over a cir cuit arrangement between two two-wire lines, the saidfcircuit arrangement beingadapted to provide repeater paths over either one `of two branch circuits, the arrangement being such that neither branch circuit is normally connected with both said two wireY lines,Y switching means being provided' and adapted to controlthe con-r nections of the two-wire lines to bothf'input and output terminals of the branch circuits.

` According to a further feature of the invention, the connecting of the branch circuitbetween the said two two-wire lines is effected byv an incoming telephone current which is adapted to be amplified over saidbranch.

Other features of the invention will be disclosed in the following description having reference tothe accompanying drawings, `in which: Fig. 1 illustrates schematically one embodiment of theinvention. 1 y

.Fig 2 illustrates a modification of the arrangement shown in Fig. 1. v

. Fig. 3 shows in morejdetail the construction of a relay which Ymay be used in the circuit arrangement of Figs. 1 and 2, Y

Fig.' 4 shows an embodiment ofthe invention in which a one way repeater is .used for amplifyving currents in both directions of transmission.

Fig. 5 is a inodiiication of Fig. 4.

Fig. 6 is a still further modification of the arrangement shown in Fig. 4. l

Fig. 1,`VW and l1." represent the points at which the circuit, in which amplification is required, enters the amplifierstation. 1,k 2, 3 and 4 are one way amplifying devices, the direction of amplication being indicated by the arrows. 5 and 6 are amplier detectors which cause opferating currents to flow respectively through the coils 7 and V10 `of the relays 11 and 14, when speech voltages of the necessary amplitude are applied to their inputs.l l5 is adelay network having a characteristic impedance which is subyby the" output ofVV the corresponding detectorstantially a pure resistance. 16 and 17 are three 'winding transformers, known in the art as hybrid coils. 18 and 19 are resistances equal to the characteristic impedance of the delay net- `work. The hybrid coils are wound ina known 30 manner so ythat currents in the output of ampiiiierY 1 apply no currents or` only' attenuated currents to the input of 4 and in the ouput of amplifier 3v apply no current kor only attenuated currents to the inputof 2. The normal or unoperated position of the contacts of relays 11 i and 14 is as shown.

In the non-operated position of the relays the system, as shown on the schematic, is stable and free from oscillation becausev there is'no 70. complete back coupling path from theoutput'to the input of any amplifier orcascade combinationof amplifiers It is assumed that capacity, through the relay` 11, between the output of amplifier 4 andthe input of amplifier ,l is ef- 7.5, iectively eliminated. Similarly, capacity, through Vrelay 14, between the output of t 2 and input` of '3 is effectively eliminated. Means for accom.-Vv vplishing this are described below.

The method of operation is as follows: t Speech currents arriving` at W pass through amplifier 1 and are simultaneously applied to the "input of the detectorv amplifier 6 Vand the dem .The process of switching the line E from the input of 3 tothe output of 2 also prevents speech currents comingffrom the'other direction from laffecting the switching gear and gives the control of the line to the speaker applying speech at W.

By a similar trainof operations speech arriving from Eispassed out at; W, thespeaker applying speech to E retaining control of the line. Speechl entering at `W is at a sufliciently high level to operate the detector amplifier 6, but is so attenuatedY by the delay networks and-hybrid l coils that it is-'not at a suiiiciently high level to operate detector amplifier 5. AThe converse isevidently true for speech entering at E; The second arrangement differs from the first by the fact that thev two hybrid coils are each replaced by @relay (12 Vor 13 Figure 2), worked *no ampliiier, in parallel with the relays 11 or 14. The effect of the four relays is that the two sec- Y ond stage amplifiers 2 ande are disconnected, and

no through conversational circuit exists, until -the arrival of speech currents results in the operation oi' two of the 4' relays. Thus in the normal or unoperated condition the device is evidently stable. Speechr currents arriving at W, are ampliiied by'l and pass to the delay network 15, and also to the output or" the detector-ampliiier 5 which causes the ope ation of relays 13 and 14. Ihe time of operation of these relays is arranged to be less than the vdelay of 15, so that by the time the network is traversed by the speech current the relays have operated, and the amplier 2 is switched in to connect the delay network to the line E. The relay 14 when operated prevents speech in the direction E---W taking placeY before that in the iff-E is nnisned, and relay 13 prevents the speech currents from the delay networkreaching detector amplifier 5. In the operated condition the device is thereby stable and it also acts as an echo suppressor.

A similar train or operations, provides for speech entering at E to be amplied to the .linel W. As in the first arrangement it is necessary, in order to avoid oscillation, that there be only small capacity coupling between amplifiers l and 4, and 2 and Y Y Fig.' 3 indicates a method Vof construction o relays 11, 12, 13 and i4 which this capacitycan be reduced as. far as possible.

The general construction or the relay 'armature 2G and coil V27k is the'nsnal construction, but

the contact springs 2l 23 to which the leads to oneampliiier, and 22 and 24 to which the leads to the other ampliier are attached are screened in pairs. The springs 2@ and 25 make contact with 21, 22, 23 and 24 through small holes in the screens. VThe leads from the amplifiers are made with screened wire, the covering o1 which together with the screens on the relays are connected to some suitable earthing point.

'currents arriving at W are amplified by Bland pass to 34, a suitable delay network. The input of an amplierY detector 35 istaken from the penultimate stage of ampliiier 31and the output operates relay 37, on the arrival of speech currents at W. Relay 37 disconnects line E from its iirst stage amplifier andconnects it to the outputl of the power amplifier. Thus by the time the speech currents have traversed the delay network, relay 37 has operated, and the conversational circuit for the direction W-E is made. Whilst speech is travelling in this direction relay 37 remains operated and speech in the opposite direction' is rendered impossible and echo thereby suppressed. The speaker at the W end'retains control of the circuit. 'When relay 37 is again normal speech in the direction E-W Vcan .take place, and resultsin asimilar Ytrain of operations;

l Provided that capacities in relays 37 and 38 are reduced to a by means such as were described above, there no singing circuit and the device is stable both in the normal and in 'two 48 and 44 by detector 46. Yspeech voltages at VV results in the operation of 39 and 4G, by which the input of the common f when conversation is in the direction W--E which it would do were it connected to the last stage of 32.` A' similar remark applies to the detector amplier 35.

"Fig, 5 shows a similar device containing four relays, two 39 and 40 worked'by detector 45 and. The arrival of power ampliiier 43 is connected to the further end or" the delay network 41 and the output to the line-E. As before the input of 46 is taken fromY some intermediate stage of amplirlier 2 so that the operation of relays 48 and 44 during conversation W--E is prevented. The same remarks concerning control, stability and echo suppression, asin Fig.'4 apply here.

Fig. 6 shows alvariation of method of Fig. 5 in which the necessity of taking the inputs of the amplier detectors from an intermediate stage oi the rst stage anrpliers is obviated. Speech currents arriving at W are ampliiied by 57, and finding 'relay 54 normal pass into the delay network 5l. By the time that the network` is traversed, detector 55 has operated relays 49 and 50 and the speech currents pass via the power ampliiier and to line E. ampiiiier 56 is broken so thatrrelays 58 and54 are prevented from operating during conversation VII-E. The same remarks COncerningcOntrOl, stability and echo suppression as in the above cases, alsoapply here. l v f Q As is now well known the electricV charges in a conductor are in a state or thermal agitation, in thermodynamic equilibrium with the heat motion of the atoms oi the, conductor. This phenomenon manifests itself as a iluctuation ci potential difference between` the terminals or the conductor and the eiiiectvproduced in an ampliiier, due to connection `of the conductor to the input side of the ampliier or to thermal agitation within the amplineritself is known as Johnson noise. For a more detailed description of the phenomenon reference may be had to the Physical Review, vol'. 32, July 1928, Vpage 97, and the Philosophical Magazine, vol. 7, 1929,

page774.`

The arrangement shown in Fig.` 6 is particularly advantageous in those ,cases where the E. M. F. of thermal agitation in the amplifiers becomes important. In the arrangement shown in Figures 4 and 5 the delay network is subjected to noise from both ampliers 31 Vand 32 and 47 and 42 respectively during both idle and talking periods. In Fig. 6 eitherampliiier 57 or amplifier 52 is disconnected from the delay network thus respectively. The points of connection of detector ampliers 35 and 36 toY ampliiiers 3l and 32 would be suitable for this purpose.

icc

Thercircuit to detector What is claimed is: 1. In a transmission system the combination of two lines each provided with switching :mecha-V nism, two branch circuits provided with two ampliers, one branch circuit for each of said lines, a conversation path common to said lines including a delay net-work, means controlled over one of said lines for operating the switching mechanism of the second line through both of said amplifiers of one of said branch circuits, means controlled by said operated switching mechanism for connecting a third amplier to the common conversation path, and means controlled by said delay network for retarding voice currents transmitted over the rst mentioned line until after the operation of the switching mechanism of the second line.

2. In a transmission system the combination of two lines each provided with switching mechanism, two branch circuits provided with two ampliiiers, one branch circuit for each of said lines, a conversation path common to said lines including a delay net-work, means controlled over one of said lines for operating the switching mechanism of the other line through both of said amplifiers of one of said branch circuits, means controlled by said operating switching mechanism for connecting a third amplifier to the common conversation path, means controlled by said delay net-work for retarding voice currents transmitted over the first mentioned line until after the operation of the switching mechanism of the second line, the operation of said switching mechanism serving to form a conversation path between both of said lines through one of said first mentioned amplifiers the conversation path, the delay net-work and third amplier.

3. In a transmission system the combination of two lines'each provided with switching mechanism, two branch circuits provided with two ampliers, one branch circuit for each of said lines, a conversation path common to said lines including a delay network, means controlled over one of said lines for operating the switching mechanism of the other line through both of said amplifiers of a branch circuit, means controlled by said operating switching mechanism for connecting a third amplifier to the common conversation path, means controlled by said delay net-work for rev'tarding voice currents transmitted over the first lines through oneof said rst mentioned ampliners the delay net-work andthird amplier, the

operation of the switching mechanism also servy ing to disconnect its associated line from its own branch circuit.

4. In a transmission system two 2-wire lines, two branch circuits adapted `to amplify in opposite directions, a switch which normally disconnects one 2-wire line from one branch circuit, another switch which normally disconnects the other Z-wire line from the other branch circuit each of said switches normally connecting a branch circuit with one two-wire line, means whereby said switches may reverse the connections so as to control the connections to both the input and output terminals of said branch circuits and a delay network common to said branch circuits.

5. A transmission system according to claim 4 wherein the delay network is connected to the branch circuit over a hybrid coil.

6. A transmission system according to claim 4 wherein the delay network is connected to the branch circuits over two additional switches controlled one from each 2-wire line.

'7. A transmission system according to claim 4 comprising two additional switches adapted to connect the delay network to the branch circuits i 

